Color image forming apparatus

Abstract

A color image forming apparatus comprises developing units each of which contains a developer of each of three primary colors, and another developing unit containing a white developer. An image on the original is subjected to color separation to obtain image density data corresponding to each primary color, and when all the density data are lower than a predetermined value, the density data are multiplied by a predetermined ratio, and a predetermined density of a white image is set. Based on the multiplied data of each color a developed image corresponding to the image density data of each primary color is formed on a recording material, and a white image corresponding to the white color density data is on the same recording material, thereby reproducing clear pastel or halftone color images.

What is claimed is: 
     
       1. An apparatus for producing a color image on a recording material, the apparatus comprising: first developing units each of which contains a developer of each of at least three primary colors;   a first means for effecting a color separation of an image on an original to output image density data corresponding to each primary color;   a second means for comparing the image density data with a predetermined value, multiplying the image density data by a predetermined ratio depending on the results of the comparison, and setting a predetermined density of a white image;   a second developing unit containing a white developer; and   a third means for controlling the formation of an image with said first developing units and said second developing unit, said third means including means for operating the second developing unit in response to the image density data obtained from the second means.   
     
     
       2. An apparatus as defined in claim 1, wherein the second means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to the at least three primary colors are lower than the predetermined value. 
     
     
       3. An apparatus as defined in claim 1, wherein the second means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to a selected one or more colors of the at least three primary colors are lower than the predetermined value. 
     
     
       4. An apparatus as defined in claim 3, wherein the at least three primary colors are yellow, magenta and cyan, and the selected one or more colors are two of them including at least one of magenta and cyan. 
     
     
       5. An apparatus as defined in claim 1, wherein the third means includes means for obtaining a binary image data from the image density data. 
     
     
       6. An apparatus as defined in claim 1, wherein a magnification of the image density used in the second means is substantially equal to the reciprocal of the reduction ratio of the density of a primary color owing to development by said white developer. 
     
     
       7. An apparatus for producing a color image on a recording material, the apparatus comprising: first developing units each of which contains a developer of each of at least three primary colors;   a first means for effecting a color separation of an image on an original to output image density data corresponding to each primary color;   a second means for comparing the image density data with a predetermined value, multiplying the image density data by a predetermined ratio depending on the results of the comparison, and setting a predetermined density of a white image;   a second developing unit containing a white developer;   a third means for controlling the formation of an image with said first developing units and said second developing unit, said third means including means for operating the second developing unit in response to the image density data obtained from the second means;   means for generating a signal indicating that the recording material is a synthetic resin film; and   a controlling means for keeping the second means out of operation in response to the signal indicating that the recording material is a synthetic resin film.   
     
     
       8. An apparatus as defined in claim 7, wherein the signal generating means is a switch operable from outside the apparatus. 
     
     
       9. The apparatus as defined in claim 7, wherein the signal generating means is a light reflector type of sensor disposed in a path along which the recording material is transported. 
     
     
       10. An apparatus as defined in claim 7, wherein the second means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to the at least three primary colors are lower than the predetermined value. 
     
     
       11. An apparatus as defined in claim 7, wherein the second means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to a selected one or more colors of the at least three primary colors are lower than the predetermined value. 
     
     
       12. An apparatus as defined in claim 11, wherein the at least three primary colors are yellow, magenta and cyan, and the selected one or more colors are two of them including at least one of magenta and cyan. 
     
     
       13. An apparatus as defined in claim 7, wherein the third means includes means for obtaining a binary image data from the image density data. 
     
     
       14. An apparatus as defined in claim 7, wherein a magnification of the image density used in the second means is substantially equal to the reciprocal of the reduction ratio of the density of a primary color owing to development by said white developer. 
     
     
       15. An apparatus for producing a color image on a recording material, the apparatus comprising: first developing units each of which contains a developer for each of at least three primary colors;   a first means for effecting a color separation of an image on an original to output image density data corresponding to each primary color;   a first density setting means for comparing the image density data with a first predetermined value and effecting an under-color removal depending on the results of the comparison;   a second density setting means for comparing the image density data with a second predetermined value and multiplying the image density data by a predetermined ratio depending on the results of the comparison, and setting a predetermined density of a white image;   a second developing unit containing a white developer;   a first controlling means for controlling the formation of an image using the first developing units but without using the second developing unit in response to density data provided by the first density setting means; and   a second controlling means for controlling the formation of an image using the second developing unit in response to density data provided by the second density setting means.   
     
     
       16. An apparatus as defined in claim 15, wherein the first predetermined value is larger than the second predetermined value. 
     
     
       17. An apparatus as defined in claim 15, wherein the first density setting means performs the under-color removal for a picture element whose image density data corresponding to the at least three primary colors are higher than the first predetermined value. 
     
     
       18. An apparatus as defined in claim 15, wherein the second density setting means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to the at least three primary colors are lower than the second predetermined value. 
     
     
       19. An apparatus as defined in claim 15, wherein the second density setting means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to a selected one or more colors of the at least three primary colors are lower than the second predetermined value. 
     
     
       20. An apparatus as defined in claim 19, wherein the at least three primary colors are yellow, magenta and cyan, and the selected one or more colors are two of them including at least one of magenta and cyan. 
     
     
       21. An apparatus as defined in claim 15, wherein a magnification of the image density used in the second density setting means is substantially equal to the reciprocal of the reduction ratio of the density of a primary color owing to development by said white developer. 
     
     
       22. An apparatus as defined in claim 15, wherein the first means includes a section in which masking is carried out. 
     
     
       23. An apparatus for producing a color image on a recording material, the apparatus comprising: first developing units each of which contains a developer for each of at least three primary colors;   a first means for effecting a color separation of an image on an original to output image density data corresponding to each primary color;   a first density setting means for comparing the image density data with a first predetermined value and effecting an under-color removal depending on the results of the comparison;   a second density setting means for comparing the image density data with a second predetermined value and multiplying the image density data by a predetermined ratio depending on the results of the comparison, and setting a predetermined density of a white image;   a second developing unit containing a white developer;   a first controlling means for controlling the formation of an image using the first developing units but without using the second developing unit in response to density data provided by the first density setting means;   a second controlling means for controlling the formation of an image using the second developing unit in response to density data provided by the second density setting means;   means for generating a signal indicating that the recording material is a synthetic resin film; and   a controller which controls the second density setting means to be out of operation in response to the signal indicating that the recording material is a synthetic resin film.   
     
     
       24. An apparatus as defined in claim 23, wherein the first predetermined value is larger than the second predetermined value. 
     
     
       25. An apparatus as defined in claim 23, wherein the first density setting means performs the under-color removal for a picture element whose image density data corresponding to the at least three primary colors are higher than the first predetermined value. 
     
     
       26. An apparatus as defined in claim 23, wherein the second density setting means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to the at least three primary colors are lower than the second predetermined value. 
     
     
       27. An apparatus as defined in claim 23, wherein the second density setting means performs the multiplication and the predetermined white image density setting for a picture element whose image density data corresponding to a selected one or more colors of the at least three primary colors are lower than the second predetermined value. 
     
     
       28. An apparatus as defined in claim 27, wherein the at least three primary colors are yellow, magenta and cyan, and the selected one or more colors are two of them including at least one of magenta and cyan. 
     
     
       29. An apparatus as defined in claim 23, wherein a magnification of the image density used in the second density setting means is substantially equal to the reciprocal of the reduction ratio of the density of a primary color owing to development by said white developer. 
     
     
       30. An apparatus as defined in claim 23, wherein said first means includes a section in which masking is carried out. 
     
     
       31. An apparatus for forming electrostatic latent images on an electrostatic latent image carrier corresponding to respective color components, developing the latent image with respective color developers, and transferring each developed image onto a recording material thereby to obtain a multi-color image, the apparatus comprising: a plurality of first developing units each of which contains a developer of each of three primary colors;   a second developing unit containing a white developer;   a first means for effecting a color separation of an image on an original to output image density data corresponding to each primary color;   a second means for comparing the image density data with a predetermined value; and   means for alternatively controlling a first copying mode or a second copying mode, wherein the first copying mode is to form electrostatic latent images corresponding to the three primary colors, develop them by use of the plurality of first developing units, and transfer the developed images onto the recording material, when the second means finds that the image density data are higher than the predetermined value, and wherein the second copying mode is to form electrostatic latent images corresponding to the three primary colors and a white color, develop these images by use of the plurality of first developing units and the second developing unit, and transfer the developed images onto the recording material when the second means finds that the image density data are lower than the predetermined value.